
midclass values
The following table gives the ages in completed years of 141 persons in a town involved in road accidents during a particular year.
Ages (years): 1215, 1620, 2125, 2630, 3140, 4150, 5170
Frequency: 15, 48, 28, 17, 14, 7, 12
Find estimates of the mean and standard deviation of the ages.
OK so my main problem is finding midclass values; since the ages are in COMPLETED YEARS the class boundaries would be 12<=x<16, 16<=x<21, etc., giving midclass values 14, 18.5, 23.5, 28.5, 36, 46, 61.
Is this correct? Cos I got mean=26.6 and the answer is 26.9, and I’m sure my calculations are correct, the problem must be with the midclass values. I also calculated the standard deviation for these midclass values and it is way off.